public RackDTO createNew(RackDTO requestDTO) {
    Merchant currectMerchant = authService.getCurrentMerchant();

    // validates if in db rack name already exist
    Rack rackInDB = rackDAO.findByMerchantAndNameIgnoreCase(currectMerchant, requestDTO.getName()).orElse(null);
    if (rackInDB != null) {

        log.error("rack with name [{}] under merchant [{}] already exist");
        return null;
    }

    Rack newRack = modelMapper.map(requestDTO, Rack.class);
    newRack.setMerchant(currectMerchant);
    newRack.setTotalCell(requestDTO.getXaxis() * requestDTO.getYaxis());
    newRack.setStatus(GeneralStatus.ACTIVE);
    rackDAO.save(newRack);

    // TODO create corresponding cell records
    for (int i = 1; i <= requestDTO.getXaxis(); i++) {
        for (int j = 1; j <= requestDTO.getYaxis(); j++) {

            Cell newCell = new Cell();
            newCell.setMerchant(currectMerchant);
            newCell.setCellId("RK" + newRack.getId() + "CL" + i + j);
            newCell.setStatus(CellStatus.EMPTY);
            newCell.setRack(newRack);
            cellDAO.save(newCell);
        }
    }
    ;

    return modelMapper.map(newRack, RackDTO.class);
}

我想为for循环中的每个单元格生成条形码，同时生成单元格id。
对免费条形码库有什么建议吗？